1. Field of the Invention
This invention relates to a furnace system suitable for use with a boiler using pulverized coal as a fuel for monitoring or controlling flames produced by the combustion of the pulverized coal or for controlling an exhaust treating apparatus connected to the boiler.
2. Description of the Prior Art
Generally, it has hitherto been usual practice to effect control of the flames produced by the combustion of a fuel in a boiler by a method wherein components of exhaust gases are analyzed and a signal is outputted to a control system in accordance with the results of the analyses performed.
Assume that it is desired to determine the concentration of the oxides of nitrogen (hereinafter NOx) in the exhaust gases, for example. To this end, it has been usual practice to introduce exhaust gases from a flue to various types of NOx meters to determine the concentration of the NOx. When it is impossible to directly lead the exhaust gases to the measuring instruments, sampling syringes resembling hypodermic syringes are used for collecting samples of the exhaust gases from the flue and the collected samples are fed into the sample inlets of the NOx measuring instruments to determine the concentration of NOx. Regardless of which method is used, samples of the exhaust gases are collected and analyzed to produce a control signal based on the results of the analysis, to thereby control the exhaust emission of the boiler. In addition to NOx, carbon monoxide, oxygen and sulfurous acid gas are noxious components of the exhausts that should be monitored. These gases have also been controlled by analyzing the exhaust gases led from the flue and producing control signals based on the results of the analyses. However, this method has suffered the disadvantage that since the exhaust gases are actually led from the flue to the measuring instruments, difficulties are experienced in coping with a sudden change in the conditions of combustion which might occur when the flames are converted to nonsteady flames that have lifted from the burner tip.
Another problem that should be grappled with when pulverized coal is used as a fuel is that it is important to minimize the amount of non-combusted coal in the ash from the point of view of avoiding environmental pollution and saving resources. When flames are produced by combusting pulverized coal, it is necessary that control of the flames be effected by monitoring the same to keep the combustion in a condition of the high efficiency by minimizing the amount of non-combusted coal. To determine the amount of non-combusted coal in the ash, it has hitherto been usual practice to collect samples of ash directly from the flue and measure the weight of a predetermined amount of ash, and then burn the samples of ash in perfect combustion in oxygen atmosphere (heating the sample ashes to 850.degree. C. by raising the temperature 10.degree.-20.degree. C. every minute to perform combustion) before measuring the weight again. Thus, the amount of the non-combusted coal is determined by deducting the weight of the ash obtained by the perfect combustion from the weight of the ash before subjected to the perfect combustion. This process is time-consuming and troublesome because it involves the use of a differential heat indicating balance and other instruments in a multiplicity of steps, so that it is impossible to effect control of flames in on-line real time control operations by feeding back the amount of non-combusted coal determined in the ash. Thus, it is also impossible for this method to cope with a sudden change in the conditions of combustion.
The methods of the prior art described hereinabove are intended to effect control of the flames produced by the combustion of the pulverized coal by relying on the analysis of exhaust gases or dust collected at the outlet of the combustion furnace. Therefore, it is impossible for these methods to take necessary measures by coping with a sudden change in the conditions of combustion. In view of the foregoing, one might think of making observations of the flames themselves in an effort to perform control as precisely as possible. More specifically, a control method may be used wherein one would keep the flames in an optimum condition by controlling the conditions of combustion based on the distribution of the concentration of gases and the distribution of temperature in the vicinity of the flame port of the burner. Usually, the distribution of the concentration of gases in the vicinity of the flame port of the burner is determined by inserting a sampling probe in the flames and obtaining samples of gases for testing, and the distribution of temperature is determined by inserting thermocouples in the flame. However, it is difficult to make accurate determinations by these methods because the flames are disturbed. In determining the distribution of the gases by obtaining their samples, the components of the gases in each of the sampling probes might react with each other (2CO+O.sub.2 .fwdarw.2CO.sub.2, for example), thereby making it impossible to accurately determine the distribution of the gases. Difficulties would also be experienced in determining the temperature distribution because of changes in temperature which might possibly occur due to radiation of heat by the furnace walls in addition to changes in the temperature of the flames themselves. All in all, it would be considered difficult to accurately determine the conditions of combustion by the methods of the prior art which rely on information including the distribution of the concentration of gases in the vicinity of the flame port of the burner and the distribution of temperature in the furnace.